Fibrocytes enhance mammary gland fibrosis in obesity.

Obesity rates continue to rise, and obese individuals are at higher risk for multiple types of cancer, including breast cancer. Obese mammary fat is a site of chronic, macrophage-driven inflammation, which enhances fibrosis within adipose tissue. Elevated fibrosis within the mammary gland may contribute to risk for obesity-associated breast cancer. To understand how inflammation due to obesity enhanced fibrosis within mammary tissue, we utilized a high-fat diet model of obesity and elimination of CCR2 signaling in mice to identify changes in immune cell populations and their impact on fibrosis. We observed that obesity increased a population of CD11b+ cells with the ability to form myofibroblast-like colonies in vitro. This population of CD11b+ cells is consistent with fibrocytes, which have been identified in wound healing and chronic inflammatory diseases but have not been examined in obesity. In CCR2-null mice, which have limited ability to recruit myeloid lineage cells into obese adipose tissue, we observed reduced mammary fibrosis and diminished fibrocyte colony formation in vitro. Transplantation of myeloid progenitor cells, which are the cells of origin for fibrocytes, into the mammary glands of obese CCR2-null mice resulted in significantly increased myofibroblast formation. Gene expression analyses of the myeloid progenitor cell population from obese mice demonstrated enrichment for genes associated with collagen biosynthesis and extracellular matrix remodeling. Together these results show that obesity enhances recruitment of fibrocytes to promote obesity-induced fibrosis in the mammary gland.

Modeling of Mouse Experiments Suggests that Optimal Anti-Hormonal Treatment for Breast Cancer is Diet-Dependent.

Estrogen receptor positive breast cancer is frequently treated with anti-hormonal treatment such as aromatase inhibitors (AI). Interestingly, a high body mass index has been shown to have a negative impact on AI efficacy, most likely due to disturbances in steroid metabolism and adipokine production. Here, we propose a mathematical model based on a system of ordinary differential equations to investigate the effect of high-fat diet on tumor growth. We inform the model with data from mouse experiments, where the animals are fed with high-fat or control (normal) diet. By incorporating AI treatment with drug resistance into the model and by solving optimal control problems we found differential responses for control and high-fat diet. To the best of our knowledge, this is the first attempt to model optimal anti-hormonal treatment for breast cancer in the presence of drug resistance. Our results underline the importance of considering high-fat diet and obesity as factors influencing clinical outcomes during anti-hormonal therapies in breast cancer patients.

Breast cancer microenvironment and obesity: challenges for therapy.

Women with obesity who develop breast cancer have a worsened prognosis with diminished survival rates and increased rates of metastasis. Obesity is also associated with decreased breast cancer response to endocrine and chemotherapeutic treatments. Studies utilizing multiple in vivo models of obesity as well as human breast tumors have enhanced our understanding of how obesity alters the breast tumor microenvironment. Changes in the complement and function of adipocytes, adipose-derived stromal cells, immune cells, and endothelial cells and remodeling of the extracellular matrix all contribute to the rapid growth of breast tumors in the context of obesity. Interactions of these cells enhance secretion of cytokines and adipokines as well as local levels of estrogen within the breast tumor microenvironment that promote resistance to multiple therapies. In this review, we will discuss our current understanding of the impact of obesity on the breast tumor microenvironment, how obesity-induced changes in cellular interactions promote resistance to breast cancer treatments, and areas for development of treatment interventions for breast cancer patients with obesity.

Alterations in the mammary gland and tumor microenvironment of formerly obese mice.

BACKGROUND: Obesity is a risk factor for breast cancer, and women with obesity that develop breast cancer have a worsened prognosis. Within the mammary gland, obesity causes chronic, macrophage-driven inflammation and adipose tissue fibrosis. Weight loss is a recommended intervention to resolve obesity, but the impact of weight loss on the mammary gland microenvironment and in tumors has not been well identified. METHODS: To examine the effects of weight loss following obesity, mice were fed a high-fat diet for 16 weeks to induce obesity, then switched to a low-fat diet for 6 weeks. We examined changes in immune cells, including fibrocytes, which are myeloid lineage cells that have attributes of both macrophages and myofibroblasts, and collagen deposition within the mammary glands of non-tumor-bearing mice and within the tumors of mice that were transplanted with estrogen receptor alpha positive TC2 tumor cells. RESULTS: In formerly obese mice, we observed reduced numbers of crown-like structures and fibrocytes in mammary glands, while collagen deposition was not resolved with weight loss. Following transplant of TC2 tumor cells into the mammary glands of lean, obese, and formerly obese mice, diminished collagen deposition and cancer-associated fibroblasts were observed in tumors from formerly obese mice compared to obese mice. Within tumors of obese mice, increased myeloid-derived suppressor cells and diminished CD8+ T cells were identified, while the microenvironment of tumors of formerly obese mice were more similar to tumors from lean mice. When TC2 tumor cells were mixed with CD11b+CD34+ myeloid progenitor cells, which are the cells of origin for fibrocytes, and transplanted into mammary glands of lean and obese mice, collagen deposition within the tumors of both lean and obese was significantly greater than when tumor cells were mixed with CD11b+CD34- monocytes or total CD45+ immune cells. CONCLUSIONS: Overall, these studies demonstrate that weight loss resolved some of the microenvironmental conditions within the mammary gland that may contribute to tumor progression. Additionally, fibrocytes may contribute to early collagen deposition in mammary tumors of obese mice leading to the growth of desmoplastic tumors.

Investigating the complex interplay between genotype and high-fat-diet feeding in the lactating mammary gland using the Tph1 and Ldlr knockout models.

Obesity is a prevailing problem across the globe. Women who are obese have difficulty initiating and sustaining lactation. However, the impact of genetics and diet on breastfeeding outcomes is understudied. Here we explore the effect of diet and genotype on lactation. We utilized the low-density lipoprotein receptor (Ldlr-KO) transgenic mouse model as an obesity and hypercholesterolemia model. Additionally, we used the tryptophan hydroxylase 1 (Tph1-KO) mouse, recently identified as a potential anti-obesogenic model, to investigate if addition of Tph1-KO could ameliorate negative effects of obesity in Ldlr-KO mice. We created a novel transgenic mouse line by combining the Ldlr and Tph1 [double knockout (DKO)] mice to study the interaction between the two genotypes. Female mice were fed a low-fat diet (LFD; 10% fat) or high-fat diet (HFD; 60% fat) from 3 wk of age through early [lactation day 3 (L3)] or peak lactation [lactation day 11 (L11)]. After 4 wk of consuming either LFD or HFD, female mice were bred. On L2 and L10, dams were milked to investigate the effect of diet and genotype on milk composition. Dams were euthanized on L3 or L11. There was no impact of diet or genotype on milk protein or triglycerides (TGs) on L2; however, by L10, Ldlr-KO and DKO dams had increased TG levels in milk. RNA-sequencing of L11 mammary glands demonstrated Ldlr-KO dams fed HFD displayed enrichment of genes involved in immune system pathways. Interestingly, the DKO may alter vesicle budding and biogenesis during lactation. We also quantified macrophages by immunostaining for F4/80+ cells at L3 and L11. Diet played a significant role on L3 (P = 0.013), but genotype played a role at L11 (P < 0.0001) on numbers of F4/80+ cells. Thus the impact of diet and genotype on lactation differs depending on stage of lactation, illustrating complexities of understanding the intersection of these parameters.NEW & NOTEWORTHY We have created a novel mouse model that is focused on understanding the intersection of diet and genotype on mammary gland function during lactation.

Obesity reduces mammary epithelial cell TGFß1 activity through macrophage-mediated extracellular matrix remodeling.

Obesity is a risk factor for breast cancer in postmenopausal and high-risk premenopausal women. Changes within the obese breast microenvironment may increase breast cancer risk. Transforming growth factor beta-1 (TGFß1) is a major regulator of mammary epithelial stem/progenitor cells, and its activity is dysregulated under conditions of obesity. Using a high-fat diet model of obesity in mice and breast tissue from women, we observed that TGFß1 activity is reduced in breast epithelial cells in obesity. Breast ducts and lobules demonstrated increased decorin in the extracellular matrix (ECM) surrounding epithelial cells, and we observed that decorin and latent TGFß1 complexed together. Under conditions of obesity, macrophages expressed higher levels of decorin and were significantly increased in number surrounding breast epithelial cells. To investigate the relationship between macrophages and decorin expression, we treated obese mice with either IgG control or anti-F4/80 antibodies to deplete macrophages. Mice treated with anti-F4/80 antibodies demonstrated reduced decorin surrounding mammary ducts and enhanced TGFß1 activity within mammary epithelial cells. Given the role of TGFß1 as a tumor suppressor, reduced epithelial TGFß1 activity and enhanced TGFß1 within the ECM of obese mammary tissue may enhance breast cancer risk.

Weighing the Risk: effects of Obesity on the Mammary Gland and Breast Cancer Risk.

Obesity is a preventable risk factor for breast cancer following menopause. Regardless of menopausal status, obese women who develop breast cancer have a worsened prognosis. Breast tissue is comprised of mammary epithelial cells organized into ducts and lobules and surrounded by adipose-rich connective tissue. Studies utilizing multiple in vivo models of obesity as well as human breast tissue have contributed to our understanding of how obesity alters mammary tissue. Localized changes in mammary epithelial cell populations, elevated secretion of adipokines and angiogenic mediators, inflammation within mammary adipose tissue, and remodeling of the extracellular matrix may result in an environment conducive to breast cancer growth. Despite these significant alterations caused by obesity within breast tissue, studies have suggested that some, but not all, obesity-induced changes may be mitigated with weight loss. Here, we review our current understanding regarding the impact of obesity on the breast microenvironment, how obesity-induced changes may contribute to breast tumor progression, and the impact of weight loss on the breast microenvironment.

Mammary adipose stromal cells derived from obese women reduce sensitivity to the aromatase inhibitor anastrazole in an organotypic breast model.

Aromatase inhibitors are the preferred treatment for certain women with estrogen receptor (ER)-positive breast cancer, but evidence suggests that women with obesity experience aromatase inhibitor resistance at higher rates. To compare how stromal cells derived from women who are lean or obese influence response to the aromatase inhibitor (anastrazole), we incorporated patient-derived stroma in a previously characterized MCF7-derived in vitro duct model. Coculture with adipose stromal cells enabled the metabolism of testosterone (T) to E2, which induced estrogen response element activity, epithelial proliferation, and hyperplasia in MCF7 cells. The effects of T were inhibited by the ER antagonist tamoxifen and aromatase inhibitor anastrazole and were increased by the aromatase inducer dexamethasone. Primary mammary adipose stromal cells derived from women with obesity displayed increased aromatase mRNA compared with lean controls. MCF7-derived ducts cocultured with obese stromal cells exhibited higher maximal aromatization-induced ER transactivation and reduced anastrazole sensitivity, a difference not seen in 2-dimensional coculture. Finally, tamoxifen was more effective than anastrazole at reducing aromatization-induced ER transactivation and proliferation. These findings suggest that patient-specific responses to hormone therapies can be modeled and studied organotypically in vitro and add to evidence advocating obesity as a parameter to consider when identifying treatments for patients with ER-positive breast cancer.-Morgan, M. M., Arendt, L. M., Alarid, E. T., Beebe, D. J., Johnson, B. P. Mammary adipose stromal cells derived from obese women reduce sensitivity to the aromatase inhibitor anastrazole in an organotypic breast model.

Obesity reversibly depletes the basal cell population and enhances mammary epithelial cell estrogen receptor alpha expression and progenitor activity.

BACKGROUND: Obesity is correlated with an increased risk for developing postmenopausal breast cancer. Since obesity rates continue to rise worldwide, it is important to understand how the obese microenvironment influences normal mammary tissue to increase breast cancer risk. We hypothesized that obesity increases the proportion of luminal progenitor cells, which are thought to be the cells of origin for the most common types of breast cancer, potentially leading to an increased risk for breast cancer. METHODS: To study the obese microenvironment within the mammary gland, we used a high-fat diet mouse model of obesity and human breast tissue from reduction mammoplasty surgery. We identified changes in breast epithelial cell populations using flow cytometry for cell surface markers, in vitro functional assays and expression of markers on breast tissue sections. RESULTS: In both obese female mice and women, mammary epithelial cell populations demonstrated significant decreases in basal/myoepithelial cells, using either flow cytometry or cell-type-specific markers (SMA and p63). Estrogen receptor alpha (ERα) expression was significantly increased in luminal cells in obese mammary tissue, compared with control mice or breast tissue from lean women. Functional assays demonstrated significantly enhanced mammary epithelial progenitor activity in obese mammary epithelial cells and elevated numbers of ERα-positive epithelial cells that were co-labeled with markers of proliferation. Weight loss in a group of obese mice reversed increases in progenitor activity and ERα expression observed in obese mammary tissue. CONCLUSIONS: Obesity enhances ERα-positive epithelial cells, reduces the number of basal/myoepithelial cells, and increases stem/progenitor activity within normal mammary tissue in both women and female mice. These changes in epithelial cell populations induced by obesity are reversible with weight loss. Our findings support further studies to examine how obesity-induced changes in stem/progenitor cells impact breast tumor incidence and histologic tumor types.

Growth of human breast tissues from patient cells in 3D hydrogel scaffolds.

BACKGROUND: Three-dimensional (3D) cultures have proven invaluable for expanding human tissues for basic research and clinical applications. In both contexts, 3D cultures are most useful when they (1) support the outgrowth of tissues from primary human cells that have not been immortalized through extensive culture or viral infection and (2) include defined, physiologically relevant components. Here we describe a 3D culture system with both of these properties that stimulates the outgrowth of morphologically complex and hormone-responsive mammary tissues from primary human breast epithelial cells. METHODS: Primary human breast epithelial cells isolated from patient reduction mammoplasty tissues were seeded into 3D hydrogels. The hydrogel scaffolds were composed of extracellular proteins and carbohydrates present in human breast tissue and were cultured in serum-free medium containing only defined components. The physical properties of these hydrogels were determined using atomic force microscopy. Tissue growth was monitored over time using bright-field and fluorescence microscopy, and maturation was assessed using morphological metrics and by immunostaining for markers of stem cells and differentiated cell types. The hydrogel tissues were also studied by fabricating physical models from confocal images using a 3D printer. RESULTS: When seeded into these 3D hydrogels, primary human breast epithelial cells rapidly self-organized in the absence of stromal cells and within 2 weeks expanded to form mature mammary tissues. The mature tissues contained luminal, basal, and stem cells in the correct topological orientation and also exhibited the complex ductal and lobular morphologies observed in the human breast. The expanded tissues became hollow when treated with estrogen and progesterone, and with the further addition of prolactin produced lipid droplets, indicating that they were responding to hormones. Ductal branching was initiated by clusters of cells expressing putative mammary stem cell markers, which subsequently localized to the leading edges of the tissue outgrowths. Ductal elongation was preceded by leader cells that protruded from the tips of ducts and engaged with the extracellular matrix. CONCLUSIONS: These 3D hydrogel scaffolds support the growth of complex mammary tissues from primary patient-derived cells. We anticipate that this culture system will empower future studies of human mammary gland development and biology.

Form and function: how estrogen and progesterone regulate the mammary epithelial hierarchy.

The mammary gland undergoes dramatic post-natal growth beginning at puberty, followed by full development occurring during pregnancy and lactation. Following lactation, the alveoli undergo apoptosis, and the mammary gland reverses back to resemble the nonparous gland. This process of growth and regression occurs for multiple pregnancies, suggesting the presence of a hierarchy of stem and progenitor cells that are able to regenerate specialized populations of mammary epithelial cells. Expansion of epithelial cell populations in the mammary gland is regulated by ovarian steroids, in particular estrogen acting through its receptor estrogen receptor alpha (ERα) and progesterone signaling through progesterone receptor (PR). A diverse number of stem and progenitor cells have been identified based on expression of cell surface markers and functional assays. Here we review the current understanding of how estrogen and progesterone act together and separately to regulate stem and progenitor cells within the human and mouse mammary tissues. Better understanding of the hierarchal organization of epithelial cell populations in the mammary gland and how the hormonal milieu affects its regulation may provide important insights into the origins of different subtypes of breast cancer.

Defining the cellular precursors to human breast cancer.

Human breast cancers are broadly classified based on their gene-expression profiles into luminal- and basal-type tumors. These two major tumor subtypes express markers corresponding to the major differentiation states of epithelial cells in the breast: luminal (EpCAM(+)) and basal/myoepithelial (CD10(+)). However, there are also rare types of breast cancers, such as metaplastic carcinomas, where tumor cells exhibit features of alternate cell types that no longer resemble breast epithelium. Until now, it has been difficult to identify the cell type(s) in the human breast that gives rise to these various forms of breast cancer. Here we report that transformation of EpCAM(+) epithelial cells results in the formation of common forms of human breast cancer, including estrogen receptor-positive and estrogen receptor-negative tumors with luminal and basal-like characteristics, respectively, whereas transformation of CD10(+) cells results in the development of rare metaplastic tumors reminiscent of the claudin-low subtype. We also demonstrate the existence of CD10(+) breast cells with metaplastic traits that can give rise to skin and epidermal tissues. Furthermore, we show that the development of metaplastic breast cancer is attributable, in part, to the transformation of these metaplastic breast epithelial cells. These findings identify normal cellular precursors to human breast cancers and reveal the existence of a population of cells with epidermal progenitor activity within adult human breast tissues.

Anatomical localization of progenitor cells in human breast tissue reveals enrichment of uncommitted cells within immature lobules.

INTRODUCTION: Lineage tracing studies in mice have revealed the localization and existence of lineage-restricted mammary epithelial progenitor cells that functionally contribute to expansive growth during puberty and differentiation during pregnancy. However, extensive anatomical differences between mouse and human mammary tissues preclude the direct translation of rodent findings to the human breast. Therefore, here we characterize the mammary progenitor cell hierarchy and identify the anatomic location of progenitor cells within human breast tissues. METHODS: Mammary epithelial cells (MECs) were isolated from disease-free reduction mammoplasty tissues and assayed for stem/progenitor activity in vitro and in vivo. MECs were sorted and evaluated for growth on collagen and expression of lineages markers. Breast lobules were microdissected and individually characterized based on lineage markers and steroid receptor expression to identify the anatomic location of progenitor cells. Spanning-tree progression analysis of density-normalized events (SPADE) was used to identify the cellular hierarchy of MECs within lobules from high-dimensional cytometry data. RESULTS: Integrating multiple assays for progenitor activity, we identified the presence of luminal alveolar and basal ductal progenitors. Further, we show that Type I lobules of the human breast were the least mature, demonstrating an unrestricted pattern of expression of luminal and basal lineage markers. Consistent with this, SPADE analysis revealed that immature lobules were enriched for basal progenitor cells, while mature lobules consisted of increased hierarchal complexity of cells within the luminal lineages. CONCLUSIONS: These results reveal underlying differences in the human breast epithelial hierarchy and suggest that with increasing glandular maturity, the epithelial hierarchy also becomes more complex.

Pregnancy-associated breast cancers are driven by differences in adipose stromal cells present during lactation.

INTRODUCTION: The prognosis of breast cancer is strongly influenced by the developmental stage of the breast when the tumor is diagnosed. Pregnancy-associated breast cancers (PABCs), cancers diagnosed during pregnancy, lactation, or in the first postpartum year, are typically found at an advanced stage, are more aggressive and have a poorer prognosis. Although the systemic and microenvironmental changes that occur during post-partum involution have been best recognized for their role in the pathogenesis of PABCs, epidemiological data indicate that PABCs diagnosed during lactation have an overall poorer prognosis than those diagnosed during involution. Thus, the physiologic and/or biological events during lactation may have a significant and unrecognized role in the pathobiology of PABCs. METHODS: Syngeneic in vivo mouse models of PABC were used to examine the effects of system and stromal factors during pregnancy, lactation and involution on mammary tumorigenesis. Mammary adipose stromal cell (ASC) populations were isolated from mammary glands and examined by using a combination of in vitro and in vivo functional assays, gene expression analysis, and molecular and cellular assays. Specific findings were further investigated by immunohistochemistry in mammary glands of mice as well as in functional studies using ASCs from lactating mammary glands. Additional findings were further investigated using human clinical samples, human stromal cells and using in vivo xenograft assays. RESULTS: ASCs present during lactation (ASC-Ls), but not during other mammary developmental stages, promote the growth of carcinoma cells and angiogenesis. ASCs-Ls are distinguished by their elevated expression of cellular retinoic acid binding protein-1 (crabp1), which regulates their ability to retain lipid. Human breast carcinoma-associated fibroblasts (CAFs) exhibit traits of ASC-Ls and express crabp1. Inhibition of crabp1in CAFs or in ASC-Ls abolished their tumor-promoting activity and also restored their ability to accumulate lipid. CONCLUSIONS: These findings imply that (1) PABC is a complex disease, which likely has different etiologies when diagnosed during different stages of pregnancy; (2) both systemic and local factors are important for the pathobiology of PABCs; and (3) the stromal changes during lactation play a distinct and important role in the etiology and pathogenesis of PABCs that differ from those during post-lactational involution.

Normal and neoplastic nonstem cells can spontaneously convert to a stem-like state.

Current models of stem cell biology assume that normal and neoplastic stem cells reside at the apices of hierarchies and differentiate into nonstem progeny in a unidirectional manner. Here we identify a subpopulation of basal-like human mammary epithelial cells that departs from that assumption, spontaneously dedifferentiating into stem-like cells. Moreover, oncogenic transformation enhances the spontaneous conversion, so that nonstem cancer cells give rise to cancer stem cell (CSC)-like cells in vitro and in vivo. We further show that the differentiation state of normal cells-of-origin is a strong determinant of posttransformation behavior. These findings demonstrate that normal and CSC-like cells can arise de novo from more differentiated cell types and that hierarchical models of mammary stem cell biology should encompass bidirectional interconversions between stem and nonstem compartments. The observed plasticity may allow derivation of patient-specific adult stem cells without genetic manipulation and holds important implications for therapeutic strategies to eradicate cancer.

CCR2+ monocytes/macrophages drive steroid hormone imbalance-related prostatic fibrosis.

Benign Prostatic Hyperplasia (BPH) is a complex condition leading to Lower Urinary Tract Symptoms in aging men, characterized by cellular proliferation, smooth muscle dysfunction, inflammation, and fibrosis. While BPH is known to involve heightened macrophage infiltration, the specific contribution of infiltrating monocytes/macrophages to the disease mechanism remains uncertain. This research explores the impact of reducing circulating monocytes and subsequently limiting their tissue infiltration by using Ccr2 knockout (Ccr2-KO) mice. Ccr2-KO and wild type mice were implanted with testosterone and estradiol (T + E2, 25 mg + 2.5 mg) pellets. Urinary function was assessed via weekly void spot assays over 12 weeks, and prostatic macrophage levels were visualized and quantified in tissue sections using an F4/80 antibody. Additionally, Ki-67 staining was used to evaluate cell proliferation, and picrosirius red staining to assess collagen accumulation. Increased voiding frequency which developed in T + E2 mice, was significantly ameliorated in Ccr2-KO mice, however, both Ccr2-KO and wild type (WT) mice showed increased bladder weights after three month, representing a hypertrophic response to bladder outlet obstruction. T + E2 substantially increased the density of macrophages in WT but not Ccr2-KO mouse prostate. Proliferation rate, as indicated by Ki-67 positivity, was elevated in the vental and anterior prostate lobes but was only marginally reduced in Ccr2-KO mice. Most importantly, a significant prostatic collagen accumulation was observed in WT mice that was markedly reduced by Ccr2 deficiency post T + E2 treatment. The absence of Ccr2 mitigates urinary dysfunction and alters prostatic macrophage levels and collagen accumulation in steroid hormone imbalance. These findings suggest a crucial role for monocyte infiltration, giving rise to macrophages or other cell derivatives, to drive fibrosis.

Gestational Intermittent Hypoxia Enhances Mammary Stem Cells and Alters Tumor Phenotype in Adult Female Offspring.

An adverse perinatal environment can increase long-term cancer risk, although the precise nature of associated perinatal triggers remain unknown. Sleep apnea is a common condition during pregnancy, characterized by recurrent cessations in breathing during sleep, and the potential consequences of sleep apnea during pregnancy as it relates to breast cancer risk in offspring have not been explored. To model sleep apnea, Sprague-Dawley dams were exposed during gestation to nightly intermittent hypoxia (GIH) or normoxia (GNx), and the mammary glands of female offspring were examined. GIH offspring demonstrated increased epithelial stem and progenitor cell populations, which are associated with diminished transforming growth factor beta (TGFß) activity. Elevations in adipose tissue stem cells in the mammary gland were also identified in GIH offspring. In aging females, mammary tumors formed in GIH offspring. These tumors displayed a dramatic increase in stroma compared to tumors from GNx offspring, as well as distinct patterns of expression of stem cell-related pathways. Together, these results suggest that exposure to sleep apnea during pregnancy leads to lasting changes in the mammary glands of female offspring. Increased stem and progenitor cell populations as a result of GIH exposure could enhance long-term breast cancer risk, as well as alter the clinical behavior of resulting breast tumors.

Prolactin promotes mammary pathogenesis independently from cyclin D1.

Epidemiological and experimental studies have revealed an important role for prolactin (PRL) in breast cancer. Cyclin D1 is a major downstream target of PRL in lobuloalveolar development during pregnancy and is amplified and/or overexpressed in many breast carcinomas. To examine the importance of cyclin D1 in PRL-induced pathogenesis, we generated transgenic mice (NRL-PRL) that overexpress PRL in mammary epithelial cells, with wild-type, heterozygous, or genetically ablated cyclin D1 in the FVB/N genetic background. Although loss of one cyclin D1 allele did not affect PRL-induced mammary lesions in nonparous females, the complete absence of cyclin D1 (D1(-/-)) markedly decreased tumor incidence. Nevertheless, NRL-PRL/D1(-/-) females developed significantly more preneoplastic lesions (eg, epithelial hyperplasias and mammary intraepithelial neoplasias) than D1(-/-) females. Moreover, although lack of cyclin D1 reduced proliferation of morphologically normal mammary epithelium, transgenic PRL restored it to rates of wild-type females. PRL posttranscriptionally increased nuclear cyclin D3 protein in D1(-/-) luminal cells, indicating one compensatory mechanism. Consistently, pregnancy induced extensive lobuloalveolar growth in the absence of cyclin D1. However, transcripts for milk proteins were reduced, and pups failed to survive, suggesting that mammary differentiation was inadequate. Together, these results indicate that cyclin D1 is an important, but not essential, mediator of PRL-induced mammary proliferation and pathology in FVB/N mice and is critical for differentiation and lactation.

Obesity and Fibrosis: Setting the Stage for Breast Cancer.

Obesity is a rising health concern and is linked to a worsened breast cancer prognosis. Tumor desmoplasia, which is characterized by elevated numbers of cancer-associated fibroblasts and the deposition of fibrillar collagens within the stroma, may contribute to the aggressive clinical behavior of breast cancer in obesity. A major component of the breast is adipose tissue, and fibrotic changes in adipose tissue due to obesity may contribute to breast cancer development and the biology of the resulting tumors. Adipose tissue fibrosis is a consequence of obesity that has multiple sources. Adipocytes and adipose-derived stromal cells secrete extracellular matrix composed of collagen family members and matricellular proteins that are altered by obesity. Adipose tissue also becomes a site of chronic, macrophage-driven inflammation. Macrophages exist as a diverse population within obese adipose tissue and mediate the development of fibrosis through the secretion of growth factors and matricellular proteins and interactions with other stromal cells. While weight loss is recommended to resolve obesity, the long-term effects of weight loss on adipose tissue fibrosis and inflammation within breast tissue are less clear. Increased fibrosis within breast tissue may increase the risk for tumor development as well as promote characteristics associated with tumor aggressiveness.

Interaction between Macrophages and Adipose Stromal Cells Increases the Angiogenic and Proliferative Potential of Pregnancy-Associated Breast Cancers.

Pregnancy associated breast cancers (PABCs) exhibit increased aggressiveness and overall poorer survival. During lactation, changes take place in the breast tissue microenvironment that lead to increased macrophage recruitment and alterations in adipose stromal cells (ASC-Ls). The interaction of these cells in PABCs could play a role in the increased aggressiveness of these cancers. We utilized an in vitro co-culture model to recreate the interactions of ASC-Ls and macrophages in vivo. We performed qRT-PCR to observe changes in gene expression and cytokine arrays to identify transcriptional changes that result in an altered microenvironment. Additionally, functional assays were performed to further elicit how these changes affect tumorigenesis. The co-culture of ASC-Ls and macrophages altered both mRNA expression and cytokine secretion in a tumor promoting manner. Tumorigenic cytokines, such as IL-6, CXCL1, CXCL5, and MMP-9 secretion levels, were enhanced in the co-culture. Additionally, conditioned media from the co-culture elevated the tumor cell proliferation and angiogenic potential of endothelial cells. These finds indicate that the changes seen in the microenvironment of PABC, specifically the secretion of cytokines, play a role in the increased tumorigenesis of PABCs by altering the microenvironment to become more favorable to tumor progression.